1. Field of Invention
The invention relates generally to the processing of semiconductor substrates, and relates more particularly to the centering of a substrate on a substrate support within a semiconductor substrate processing system.
2. Background of the Invention
Integrated circuits have evolved into complex devices that can include millions of transistors, capacitors and resistors on a single chip. The evolution of chip designs continually requires faster circuitry and greater circuit density that demand increasingly precise fabrication techniques and processes. One fabrication process frequently used is chemical vapor deposition (CVD). Chemical vapor deposition is generally employed to deposit a thin film on a substrate or a semiconductor substrate.
Chemical vapor deposition is generally accomplished by introducing a precursor gas into a vacuum chamber. The precursor gas is typically directed through a showerhead situated near the top of the chamber. The precursor gas reacts to form a layer of material on the surface of the substrate that is positioned on a heated substrate support (e.g., a heater) typically fabricated from aluminum. Purge gas is routed through holes in the support to the edge of the substrate to prevent deposition at the substrate's edge that may cause the substrate to adhere to the support. Deposition by-products produced during the reaction are pumped from the chamber through an exhaust system.
Consistency in the characteristics and quality of processed substrates is a key concern. During handoff of the substrate from a transfer mechanism (e.g., a robot) to the substrate support, or during processing, the position of the substrate may shift relative to the support, resulting in variations in the process results from substrate to substrate. Thus, substrate centering mechanisms are sometimes employed in an attempt to consistently maintain the position of each substrate relative to the support.
Incorporation of substrate centering mechanisms in the process chamber is difficult due to the sensitivity of the CVD process to mechanisms in the chamber (for example, magnetic and/or electric field characteristics) and to the hostile environment of the chamber itself. Conventional substrate centering techniques often focus on improving repeatable robot handling and have proven to be reasonably reliable and accurate; however, such techniques also tend to be costly and require complex software. Furthermore, such techniques generally address the centering of the substrate on the support during handoff from a transfer mechanism, but they typically do not account for movement of the substrate on the support, which may occur during and/or after handoff.
Therefore, there is a need for a substrate centering apparatus.